Hållbar omvandling av kaffesump till högkvalitativ biografit

Sustainable management of waste resources is a key challenge in energy engineering. Spent coffee grounds (SCG) are abundant organic waste (over eight million tons generated annually, around the world) that often end up in landfills, leading to environmental concerns and lost resource potential. This thesis examines the conversion of SCG into a high-value, graphitic carbon material of biological origin (“bio-graphite”) via a novel, multi-step thermochemical process. The process begins with drying the SCG material and subjecting it to low-temperature pyrolysis at 550 °C to obtain a carbon-rich char, followed by combined ball-milling the char with iron powder and a subsequent graphitisation heat treatment at 1300 °C. Dispersed iron particles catalyse the rearrangement of the amorphous char into well-ordered graphite layers at temperatures several hundred degrees below those typically required for graphitisation. A subsequent mild acid leach, followed by thorough water rinsing, strips out the residual metal and delivers a high-purity bio-graphite powder. Comprehensive material characterisation by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, and gas chromatography-mass spectrometry (GC–MS) was carried out. The produced bio-graphite exhibits a high degree of crystallinity (graphitisation rate ~95.6%) and a favourable carbon conversion yield (~74%), demonstrating that SCG can be upgraded into a sustainable graphite material of promising quality and yield. The results demonstrate that upgrading waste-stream biomass material can provide essential carbon resource for next-generation sustainable energy applications.